Date: Fri, 10 Sep 2010 13:45:38 +0200
From: Marius Hauki <rezycle.bin@gmail.com>
Subject: Re: [Amps] Amps Digest, Vol 93, Issue 11
Good idea to use diodes instead of drop resistor Bill. Thank you for
helping out! I would think that the diodes should be able to withstand
very large surges, as you mention in case of a glitch. If the back to
back diode combination should become open circuit (in case of a very
large glitch) and someone (not me) then removes Bminus before Bplus,
there is no return current via the chassis path to Bminus. This would
place the RF deck at Bpluss. This also would apply to a defective grid
drop resistor of course. However I am not sure if a resistor is more
likely to survive a glitch than a 6A10. I would tend to trust the
resistor, but thats just me.
## 6A10 safety diode's will never go open. They will always fail
shorted. [if they fail]. Put 2-4 of em in parallel...and in each direction,
and everything else will blow up 1st. Put 2-6 kv across a low wattage drop
resistor,
and you can kiss it good bye.
## In the old books, they used to install a 10 ohm, 10 watt WW..between B-
and
chassis..to keep the B- from wandering. Any B+ to chassis arc.. and all that
fault current
will find a path ..back to B-..... and that path takes it through the 10 ohm
resistor..which
of course explodes. IF the GG tubes being used had delicate grids in
em..sure, then perhaps
use one of the triode boards. Even then, grid overcurrent protection is easy
to implement.
## with most thoriated tungsten tubes..and simple protection, like
grid/cathode fuses, Glitch R/
1-2 HV fuses, mag hydrualic mains breaker, external Hi swr protection, plenty
of safety diodes ,
like the 6A10 variety, .... you are covered. You can even install an
adjustable spark gap..or
use a gas discharge tube on the pi-net if u want.
Later... Jim VE7RF
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